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Publication numberUS3315200 A
Publication typeGrant
Publication dateApr 18, 1967
Filing dateNov 19, 1964
Priority dateNov 20, 1963
Publication numberUS 3315200 A, US 3315200A, US-A-3315200, US3315200 A, US3315200A
InventorsWilliam Hannay Richard
Original AssigneeBritish Aircraft Corp Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Strain gauges
US 3315200 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

April 18; 1967 STRAIN GAUGES 7 Filed Nov. 19, 1964 Inventor filer/M0 WILL/19m HAW/my a a Home 1 R. w. HANNAY 3,315,200

United States Patent 3,315,200 STRAIN GAUGES Richard William Hannay, Downend, Bristol, England, assignor to British Aircraft Corporation (Operating) Limited, London, England, a British company Filed Nov. 19, 1964, Ser. No. 412,477 Claims priority, application Great Britain, Nov. 20, 1963,

5,822/ 63 1 Claim. (Cl. 338-2) Often measurements have to be taken of properties of surfaces that involve the attachment of a transducer to the surface. It is convenient, therefore, if a transducer can be provided in a transducer unit complete with means for its ready attachment to a surface and means supplying all the necessary features enabling accurate measurements to be taken. Examples of such features are electrical insulation of the element from the surface, ability of the unit to withstand high temperatures, minimum thermal resistance between the element and the surface, and minimum thermal inertia of the unit as a whole.

According to the present invention a transducer unit comprises a transducing element of electrically conducting material mounted by means of adhesive to lie between the adjacent surfaces of two metal foils, each surface having an electrically non-conducting film.

A unit having such a construction is of particular use when strain is required to be measured. In such a case, the transducing element is of the type for measuring strain and the adhesive is capable of transmitting strain.

Preferably the element is a metal foil. By the term foil is understood the form of an object having insignificant depth in comparison with its width or length even though they are obviously finite, for example a pencil line. An element of such a form is very sensitive, can be made very small, and can, therefore, take very localised measurements.

Preferably the element is of cupronickel and is of the printed circuit type. Cupronickel alloys are particularly suitable for measuring strain in the temperature range -40 to 200 C.; cupronickel alloys having particular compositions are easily and accurately produced, so that a particular composition necessary for reasons explained later is readily produced.

A printed circuit may be produced in several Ways. One entails coating a foil of metal, of suitable thickness, which is mounted by weak adhesive on a backing of plastic sheet, with a light sensitive coating, masking the portion corresponding to the area of the foil not required in the form of the element, then exposing the remainder to light. The exposed portion of the coating becomes insoluble in Water; subsequent washing removes the soluble portion, and the exposed metal is etched away; the remaining portion of the foil therefore corresponds to the element. The insoluble coating is then removed. The non-conducting films on the two metal foils between which the element is to be sandwiched are coated with adhesive. The element is then pressed onto one of the adhesive coatings, its backing is stripped off, and finally the coatings on the two metal foils are pressed together to enclose the element.

In some embodiments of this invention the adhesive is preferably of the metal-dust filled resin type, such an adhesive has a higher thermal conductivity than a basic resin.

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It is preferable in some applications to have had the transducer assembled under substantial pressure to make the thickness of the adhesive very small e.g. 0.00025 inch on each side of the element. In consequence the unit has less bulk, and the conductivity of heat between the surface and the element is improved.

Preferably at least one of the metal foils is of aluminium. This metal is readily available in foil form, has a high thermal conductivity, is light and transmits strain satisfactorily. A foil thickness of about 0.0005 inch has been found to have the necessary rigidity combined with suitable flexibility for strain transmission and thinness for good thermal conductivity.

A preferable material for a non-conducting film is aluminium oxide, since this is hard and permits pressure to be applied during assembly of the unit for the reasons explained above. A suitable thickness for this film has been found to be 0.0002 inch; considering ease of production with the hardness and degree of insulation necessary. Such a thickness of oxide is preferably commercially produced by anodic oxidation of the aluminium foil, but it is possible to achieve an oxide film of suflicient thickness by a vacuum deposition method.

It is particularly convenient, in the case of a strain gauge embodiment of the invention, if it is mounted on a surface of such material that it performs as a selected melt strain gauge. That is, the material of the gauge element is chosen such that when the element is totally and firmly attached to the particular surface, the change in resistance which is caused by the change in temperature of the element is substantially counteracted by the change in its resistance due to the change in its physical dimensions. Clearly the factors involved are the temperature coefficient of resistance of the element material, and the temperature coeificients of expansion of the materials of the element and of the surface. A further consideration is that, since these factors do not vary linearly with temperature for any materials, the materials have to be chosen to give optimum compensation for the particular temperature range required.

Preferably the transducer unit is further provided with an adhesive coating for attaching it to an independent surface. This adhesive may be of the synthetic resin type, and would have to be satisfactory in strain-transmissive properties over the working temperature range of the transducer unit. It is provided on the unit in semi-cured form, and preferably has a pressure-sensitive characteristic. Protection of the adhesive pre-coating during storage of the unit may be effected by a strip-off paper, or by plastic film backing. This pre-coating is conveniently applied during manufacture and greatly facilitates attachment.

Alternatively the unit may be attached by soldering, using a special flux in the case of aluminium. This leaves the thermal conductivity of the unit unimpaired and reduces the time to fix the unit to the surface. The time to fix an adhesive gauge is extended by the time to cure the adhesive used (e.g. 30 minutes) but the soldering operation would take only about 30 seconds.

It is considered that a transducer unit constructed according to the invention would have a performance when exposed to radiant heating under transient heating conditions, with rates as high as 6 degrees centigrade per second, insignificantly different from that under steady state heating conditions.

One embodiment of the invention, a strain gauge, is now described with reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of a strain gauge prior to assembly.

FIGURE 2 is a section through the strain gauge taken on the line 2-2 in FIGURE 1.

An element 4 is shown sandwiched between two adhesive coatings 6 and 7 on the oxide films 2 and 3 respectively, which are on the metal foils 1 and 5, respectively. The unit is mounted by means of an adhesive or solder 9 to the surface 10 of a component 8.

I claim:

A strain transducing unit for attachment by an adhesive to a member having a high fluctuating temperature, the unit comprising, in superjacent sequence, the following parts: a first aluminum foil, a first electrically insulating aluminum oxide coating, then, in substantially coplanar relationship, a cupronickel strain transducer element and portions of a resin thereon, a second electrically insulating aluminum oxide coating, and a second aluminum foil, said aluminum foils having a thickness of about 0.0005 inch, said aluminum oxide films having a thickness of about 0.0002 inch, and on the outside of one of said aluminum foils a layer of adhesive for attachment to a test specimen.

References Cited by the Examiner UNITED STATES PATENTS 2,360,267 10/1944 Osterheld 338-244 2,363,181 11/1944 Howland 338-2 2,486,822 11/1949 Cameron 165-171 X 2,492,215 12/ 1949 Osterheld 219-376 2,613,306 10/1952 Waltersdorf et a1. 219-345 2,662,957 12/1953 Eisler 338-255 X 2,799,793 7/1957 De Cain 165-180 X 2,837,619 6/1958 Stein 338-2 2,971,073 2/1961 Eisler 338-212 X 3,031,739 5/1962 Boggs 219-345 X 3,036,458 5/1962 Vali.

3,105,139 9/1963 Russell 338-2 X 3,153,140 10/1964 Theodore et a1. 219-345 X 3,274,528 9/1966 Bermann 338-2 RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2360267 *Nov 23, 1942Oct 10, 1944Mcgraw Electric CoEncased heating unit
US2363181 *Jul 12, 1943Nov 21, 1944Lockheed Aircraft CorpStrain gauge
US2486822 *Dec 23, 1946Nov 1, 1949George OrleyFreezer plate
US2492215 *Aug 14, 1946Dec 27, 1949George GreenbergToy fireboat
US2613306 *Feb 28, 1949Oct 7, 1952Gen ElectricElectrical wiring panel
US2662957 *Oct 23, 1950Dec 15, 1953Eisler PaulElectrical resistor or semiconductor
US2799793 *Oct 31, 1952Jul 16, 1957Gen Precision Lab IncElectronic tube shield
US2837619 *Aug 30, 1954Jun 3, 1958Samuel SteinStrain sensitive element and method of manufacture
US2971073 *Jul 8, 1958Feb 7, 1961Paul EislerElectric surface heating devices
US3031739 *Jun 2, 1958May 1, 1962Wiegand Co Edwin LElectric heating units and method of making the same
US3036458 *Sep 24, 1957May 29, 1962Ind Physics IncMethod and means for measuring strain in materials
US3105139 *Jun 8, 1960Sep 24, 1963Microdot IncStrain gages and installation of the same
US3153140 *Sep 12, 1961Oct 13, 1964Electric Parts CorpRadiant heating panel
US3274528 *Mar 23, 1964Sep 20, 1966Lockheed Aircraft CorpStrain measuring device
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3451030 *Jul 1, 1966Jun 17, 1969Gen ElectricSolder-bonded semiconductor strain gauges
US3639861 *Jan 24, 1968Feb 1, 1972Int Standard Electric CorpMagnetostrictive filter and strain gauge
US4310823 *Jan 14, 1980Jan 12, 1982W. C. Heraeus GmbhStrain gauge strip element and method of its manufacture
US4498337 *Feb 28, 1983Feb 12, 1985Robert Bosch GmbhTemperature sensor for determining mass transfer rate and/or temperature rate of a flowing medium
US4691117 *Mar 3, 1986Sep 1, 1987International Standard Electric CompanySwitch device
US4719443 *Apr 3, 1986Jan 12, 1988General Electric CompanyLow capacitance power resistor using beryllia dielectric heat sink layer and low toxicity method for its manufacture
US5631622 *Feb 14, 1995May 20, 1997Hottinger Baldwin Messtechnik GmbhStrain gage and measuring transducer and method of producing the same
US6152597 *Jun 26, 1998Nov 28, 2000Potega; Patrick H.Apparatus for monitoring temperature of a power source
US7059769 *Oct 27, 2000Jun 13, 2006Patrick Henry PotegaApparatus for enabling multiple modes of operation among a plurality of devices
DE4404716A1 *Feb 15, 1994Aug 17, 1995Hottinger Messtechnik BaldwinDehnungsmeßstreifen und Verfahren zur Herstellung eines Dehnungsmeßstreifens sowie Meßgrößenaufnehmer
EP0065419A1 *May 14, 1982Nov 24, 1982Crystalate Electronics LimitedStrain gauge
WO1999000004A2 *Jun 26, 1998Jan 7, 1999Patrick H PotegaApparatus for monitoring temperature of a power source
Classifications
U.S. Classification338/2, 338/212, 338/25, 374/E07.9, 338/314
International ClassificationG01L1/22, G01L1/20, H01C1/02, H01C17/07, G01K7/04, H01C17/06, G01K7/02
Cooperative ClassificationH01C1/02, H01C17/07, G01K7/04, G01L1/2287
European ClassificationG01K7/04, G01L1/22E, H01C17/07, H01C1/02
Legal Events
DateCodeEventDescription
Feb 5, 1982ASAssignment
Owner name: BAC AND BRITISH AEROSPACE, BROOKLANDS RD., WEYBRID
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:BRITISH AIRCRAFT CORPORATION LIMITED,;REEL/FRAME:003957/0227
Effective date: 19811218
Feb 1, 1982ASAssignment
Owner name: BRITISH AEROSPACE PUBLIC LIMITED COMPANY
Free format text: CHANGE OF NAME;ASSIGNOR:BRITISH AEROSPACE LIMITED;REEL/FRAME:004080/0820
Effective date: 19820106
Owner name: BRITISH AEROSPACE PUBLIC LIMITED COMPANY, DISTRICT